Let me clarify what I mean before everyone starts jumping to conclusions because maybe I have jumped to a conclusion. The conventional method of using two 45's instead of a single 90 bend is what I am referring to and not a manufactured bend in a pipe. Also the tests were done in PVC, we in Oz do very little metal ducting simply because it basically does not exist due to no HVAC industry as you guys have. Go to the Ubeaut woodworking forum and have a search through the dust extraction sub forum for the tests. There is a lot of work done in that forum looking for ways to improve flow and also looking at dust monitoring, more than anywhere else I know of. There is hours of reading there for anyone who is interested.
Chris
Everything I like is either illegal, immoral or fattening